Perhaps you should try some spelling variations:
hieu toan » bieu toan, thien toan, kiem toan
toan cau » toan cao, toan ban, toan tap
cau tren » dau tren, ca tren, cau treo
vat hanh » vat thanh, van hanh, va hanh
cau thuc » cau truc, cuu thuc, can thuc
hanh va » hang va, hanh vi
su sach » so sach
tang xa » trang xa, tang ma, lang xa
ky tang » ky nang, ky dang, kho tang
vu sach » vu bach, vu khach
cu tren » tu tren, dua tren

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: ((su sach) OR (vu sach)) ky tang xa hoi. hieu toan cau thuc vat hanh va ((cau tren) or (cu tren))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((su sach) OR (vu sach)) ky tang xa hoi. hieu toan cau thuc vat hanh va ((cau tren) OR (cu tren)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((su sach) OR (vu sach)) ky tang xa hoi. hieu toan cau thuc vat hanh va ((cau tren) or (cu tren))".
• Adding a wildcard symbol may retrieve word variants: ((su sach) OR (vu sach)) ky tang xa hoi. hieu toan cau thuc vat hanh va ((cau tren) or (cu tren))*.